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Photoshop CS4 for Photographers is an essential course for any digital photographer who wants to master the software's vast array of image enhancement techniques. Professional photographer and instructor Chris Orwig uses his own compelling images to demonstrate how the power of Photoshop can make photographers more passionate about their work. He covers many aspects of the application, such as working with RAW images, using curves and levels, making images snap, and enhancing bland photographs by converting them to black and white. Exercise files accompany this course.
Because we are interested in learning, how to create compelling photographs, because we want to create photographs that have impact, that move people that are intriguing, that are engaging, we need to do a little bit about bit depth. And what bit depth has to do with is what the digital image is actually made of. Now, is this essential information? Well, that kind of depends. Is it essential for a mechanic to know about a carburetor? Well, yes. It is essential for me to know about a carburetor? Well, probably not. I'm not a mechanic. So if we want to become a photographer or if we want to become a digital image maker and we want to make images that are interesting, we need to know a little bit about bit depth.
So here it goes. Way back in the day, James Clerk Maxwell was a guy who really came up with this first concept of a color image. Now there are a lot of different people who are trying to create color images, but here's what he did. He took this red, green and blue filter and he captured his image through these different filters and he project it through these different filters and voila! Color's actually kind of amazing. And Maxwell's discovery of using these three different colors, red, green and blue, and then shining light through these three different colors is where we get our modern understanding of color. We working in an RGB color space, red, green and blue, and let's try on this idea for a size. And if you are thinking this is a little esoteric, this is little weird, well stick with me, because I think this will become a little bit more clear as we go through this movie and as we begin to work in Photoshop more and more.
Well, in an RGB color space, color is specified by three coordinates and let's just make up these. Let's say this particular red is a mixture of 237 red, 12 green and 12 blue. And mixing those colors together gives us a specific color. Now this color in the Adobe RGB color spaces is unique. No other color combination of those numbers will get this particular color. If you change the numbers, you change a color. These numbers are derived from bit depth. Now bit depth is kind of interesting. It sounds like a strange word. It's actually not that strange, really. What bit depth is getting that is that our images are made up of pixels and the word pixels are a concatenation or combination of the two words, picture and element. And if we zoom in on an image, we see that image is really made up of these small squares. Now, where do the small squares come from? Well, a bit is a binary digit. It's again now binary means one or zero and a digit is a number. So if we have 8 bits, it's one byte; 1024 bytes equals one kilobyte, so on and so forth. So that's actually how we build up our files.
Now a bit can be compared to a light switch that can be turned on or off and quick side note-- every explanation of bit depth is going to fall little bit short, yet I think this one might help. So think of a bit as a switch that can be turned on or off. If we have a one-pixel, one-bit image it can either be on or off, it can be black or white. Then if we have a one-pixel, two-bit image, well, now we have these different gray levels. Right? We have these different combinations, so you can see that black, dark gray, light gray and then white. Well, as we move forward, let's say we have a three-bit image. We are all of a sudden almost getting into continuous tone. Well, finally when we get to eight-bits per pixel or 256 gray levels it fools the eye into appearing as though we have continuous tone. It's not real continuous tone, right? They are pixels, they are squares, yet it fools the eye into seeing that continuous tone.
Well, in this RGB color space we have eight bits of red, eight bits of green and eight bits of blue. Now the color model for photographers is this RGB space and for an image to have a four range of colors, each color channel needs to have minimum of eight bits per channel. This yields 16 million color possibilities. So again eight bits, we have this 256 gray levels. 12 bit, 4,000 levels. 14 bit, 16,000 levels. 16 bit, 65,000 levels. Now, how then does this actually relate to Photoshop? We are going to see this bit depth scale, this 0-255 scale, all over the place and here we have a screen grab of a photograph that's been modified with a Curves Adjustment and here you can see that in the 0-255 down below and to the left of the Curves Adjustment. We are also going to find this in the Levels dialog and again we have the 0-255 gray scale. So what's the big deal? Is all this stuff actually essential? Well, no it's not essential, yet it's helpful. It's helpful to know that Photoshop is based on this gray scale and that we are working in this RGB color space, which really is taking these three different channels of information, red, green and blue, and shining light through and it's a combination of those three channels that then creates the digital image.
Now initially it sounds little abstract, it sounds a little esoteric, yet as we dig in the Photoshop and as we begin to work on images you are going to start to see this bit depth topic come up more and more and by simply understanding where it's coming from it can help you make more progressive and more effective image edits.
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